1. Technical Field
The present invention relates to an improved apparatus to form a uniform continuous thin sheet of product. More specifically, this invention relates to the use of hydraulic actuators to rigidly fix the position of a movable roller relative to an opposing roller. The invention also relates to the use of thermal expansion blocks to make minute adjustments to the position of the opposing roller thereby precisely adjusting the sheeter gap.
2. Description of Related Art
In a conventional dough sheeter, opposing rollers are separated by a small gap or nip. Dough or other product material is fed into the nip above the rollers and passes through the rollers to form a sheet. In one configuration, one roller is generally fixed in a frame while an opposing roller is adjustable so that a product thickness can be selected.
One adjusting mechanism to manipulate the position of a roller consists of some form of a screw jack driven by a manual crank or electric motor. Alternatively, the adjusting mechanism may consist of other known leveraging mechanisms to implement large-scale and small-scale changes to the size of a sheeter nip. Tapered blocks may be used to fix the position of one roller relative to the other. Another commonly used mechanism to adjust nip size consists of a moveable roller attached to a pivoting frame.
A drawback of these and similar designs is that sometimes the combined deflection of the frame, adjusting mechanism, rollers, and bearings exceeds the desired gap setting for high loads and thin products. For example, in potato chip manufacturing, typical sheeter rollers can experience as much as a 0.030 inch (0.762 mm) deflection during operation which can hinder precise sheet thickness control.
Extraordinary care is usually required to assure that the rollers do not collide when there is no product in the nip of a sheeter. A sudden loss of dough feed could result in the relief of the elastic strain in the rollers, frame, and adjusting mechanism, resulting in the rollers coming into contact with each other, and being damaged thereby. Damage could also result to rollers with relatively large diameters upon a temperature change; excessive thermal expansion of mechanical parts could cause damage. For example, if the temperature of the rollers is controlled to a temperature below ambient conditions, the loss of coolant could result in both rollers naturally coming to room temperature, and for large diameter rollers, the resulting diameter change in the rollers could exceed the gap between them.
One remedy for the possible large mechanical deflection is to clamp the rollers together, and set the gap between the rollers at assembly. In such case, the amount of mechanical strain under a load could be minimized by the elimination of machine elements such as are found in the aforementioned adjusting mechanisms. One drawback to this approach is that gap changes may be made only by changing shims in the machine, a task that would require taking the machine out of production for some period of time. For large diameter rollers, especially those that are temperature controlled, this method does not protect against roller contact resulting from thermal expansion of the rollers beyond the available gap between the rollers. Therefore, damage may still be caused from large temperature changes and thermal expansion of sheeting machinery.
Consequently, a need exists for a system and a method for providing safe and effective operation of a dough sheeter having a mechanism for quickly increasing the sheeter gap in order to prevent damage to the rollers. Additionally, a need exists for a system and method to allow for improved accuracy in the adjustment of the sheeter gap, especially while sheeter rollers are in production under a load. Such a system should provide these features and should be capable of high-speed, high-capacity production. Additionally, the resulting system should be mechanically stiff so as to minimize deflections under an operating load. Such a system should provide improved precision in order to produce a thin uniform sheet of product.